1. Field of Invention
The invention relates to an electrophotographic image forming apparatus, such as a laser printer.
2. Description of Related Art
Electrophotographic image forming apparatus are well known in the art. These devices, such as a laser printer, typically include a photosensitive drum, a charger, a laser scanner, a developing roller, and a transfer roller. After the surface of the photosensitive drum is uniformly charged by the charger, the surface of the photosensitive drum is irradiated with a laser beam emitted from the laser scanner, and an electrostatic latent image is formed based on predetermined image data.
Toner carried on the developing roller is supplied to the electrostatic latent image formed on the surface of the photosensitive drum. The toner deposited on the surface of the photosensitive drum is transferred to a sheet passing between the photosensitive drum and the transfer roller.
The developing roller is rotatably attached to a developing cartridge. The developing cartridge is provided with sealing elements to prevent toner from leaking from both ends of the developing roller with respect to an axial direction thereof. The sealing elements are placed so as to make sliding contact with the circumferential surface of the developing roller, at both ends of the inside of the developing cartridge with respect to the axial direction of the developing roller when mounted in the developing cartridge in position.
When a laser printer is used for a prolonged period, toner diffuses toward an axial direction of a developing roller by the rotation of the developing roller, and gradually passes in between the developing roller and a sealing element that makes sliding contact with the developing roller. Before long, toner spreads all over the sealing element, and toner finally leaks.
The invention provides an image forming apparatus to prevent toner leakage when the image forming apparatus is used for a long term and at a high speed.
According to an aspect of the invention, to prevent toner as a developing agent from leaking from a housing of a developing cartridge, the developing cartridge as a developing agent container is provided with a sealing element. The sealing element is disposed so as to make contact with a circumferential surface of the developing roller at an end. The sealing element has a first surface and a second surface. The second surface is disposed outwardly of the first surface in the axial direction of the developing roller at a specified distance from the first surface to provide a space therebetween. To provide the spacing, a plurality of sealing elements may be disposed with a specified distance from each other at one end.
Toner that passed in between the developing roller and the first surface spreads all over the first surface as the use of the laser printer prolongs, and as a result, toner may leak from the first surface. According to another aspect of the invention, leaking toner drops in the space provided between the first surface and the second surface, but does not move in between the developing roller and the second surface. Thus, even when the laser printer is used for a long term or at a high speed for continuous image forming, toner does not leak outside the housing.
Toner is prone to pass in between the developing roller and the sealing element because the developing roller rotates. However, toner does not leak outside with a structure indicated in another aspect of the invention.
When sealing elements are provided at both ends of the developing roller with respect to the axial direction thereof, toner can be sealed at both ends where toner is prone to leak, thereby improving the toner sealability.
Preferably, the developing roller is made of an elastic member to reduce damage to a photosensitive member and toner. The developing roller made of an elastic member has difficulty carrying toner on the surface, and is apt to cause toner leakage, as compared with that of a foam member. If the developing roller is made of metal, it is also apt to cause toner leakage because the surface is easily scratched. However, with the adoption of the sealing element, toner leakage can be reliably prevented even when the developing roller is made of an elastic member, especially silicone rubber.
The first surface and the second surface make sliding contact with the circumferential surface of the developing roller, to prevent toner leakage. Further, the sealing element is made of felt, thereby reducing frictional resistance between the developing roller and the sealing element.
If the sealing element is made of a foam member such as a sponge, it may be torn due to the sliding contact with the developing roller. If the sealing element is made of an elastic member, which is not a foam member, resistance in the sliding contact becomes great, and great loads are imposed on the developing roller and the sealing element. Under this condition, when toner passes in between the developing roller and the sealing element, the toner scratches the surface of the sealing element from which toner is prone to leak.
Felt is preferably made from polyester-base fibers. Polyester-base fibers are excellent in wear resistance and durability, thus, the sealing element resists damage during continuous use, so that toner leakage can be reliably prevented.
It is preferable that a thickness of each of the fibers for felt is smaller than or equal to 2.1 times as large as a mean particle diameter of toner. Such fine fibers resist damage and reliably absorb toner because they are tangled closely, thereby reliably preventing toner leakage.
The first surface and the second surface are coated with a fluorine-base lubricating agent including a fluorine oil and fluorine-base resin. The lubricating agent works between the developing roller and the sealing element, reducing resistance to the sliding contact. Thus, the wear resistance and the durability of the sealing element are improved and noise due to the sliding contact are prevented from generating. Especially, as the fluorine-base lubricating agent includes fluorine oil and fluorine-base resin, it greatly contributes to an effect of reducing the frictional resistance.
As toner, prepared polymerized toner may be used. Polymerized toner has a uniform particle size of 5-10 xcexcm, is excellent in the flowability, and suitable to form high quality images. Polymerized toner tends to pass in between the developing roller and the sealing element, becoming a cause of toner leakage. However, with the structure of the invention, toner leakage can be reliably prevented.
To assemble the above developing cartridge, the sealing elements are placed inside the housing, the developing roller is placed, from a direction parallel to the direction that the developing roller feeds toner, on the first surface and the second surface, and bearings are mounted at both ends of the developing roller from outside the housing.
If the developing roller is placed, from a direction parallel to the axial direction of the developing roller, on the first surface and the second surface, the circumferential surface of the developing roller, the first surface, and the second surface are rubbed in the axial direction of the developing roller. To avoid increasing the size of the developing cartridge, the first surface and the second surface should be made narrow. In this case, they are weak in rigidity, and liable to deform. The deformation of the sealing element causes toner leakage.
However, in the assembling method, the developing roller is placed on the first surface and the second surface from the direction parallel to the direction that the developing roller feeds toner, and thus, the first surface and the second surface do not receive a force causing these surfaces to be deformed. As a result, there is little likelihood of toner leakage due to the deformation of the sealing elements.